1. Field of the Invention
This invention relates to pneumatic studless tires, and more particularly to a studless tire having a tread provided with a plurality of circumferential grooves arranged at given intervals in a widthwise direction of the tire and extending in a circumferential direction of the tire or substantially in the circumferential direction, a plurality of lateral grooves arranged at given intervals in the circumferential direction and extending in the widthwise direction or substantially in the widthwise direction, many blocks defined by these circumferential grooves and lateral grooves and a plurality of wave-shaped sipes formed in each block and extending substantially in the same direction as in the lateral groove, and using on snow and ice road surfaces.
2. Description of Related Art
In a studless tire used on snow and ice road surfaces, when a plurality of lateral sipes are formed in each of the blocks defined by plural circumferential grooves extending in the circumferential direction and plural lateral grooves crossing these circumferential grooves, water film is cut by the lateral sipes to improve the running performance on ice. However, if it is intended to more improve the running performance on ice by increasing the number of lateral sipes, the rigidity of the block itself considerably lowers and hence the running performance on ice inversely lowers.
For this end, it is difficult to improve the running performance on ice of the studless tire above a certain level by conventional technique.